What exactly is "exact" (was Clean Singleton Docstrings)

[Rustom Mody]

On Monday, July 18, 2016 at 10:16:58 AM UTC+5:30, Ben Finney wrote:

> You will be able to express yourself much more clearly on this topic
> when you cease conflating a number with measurements of that number, or
> conflating a number with representations of that number.
> 

That more or less sums up (my understanding of) scheme's intent of having 
the exact/inexact classification: An inexact number is a measured/observed 
number with that data intentionally preserved.
An exact number is just a mathematic number ie a plain ol' number

>From the scheme docs I earlier quoted: 

| [Motivation for (in)exact...]  the inexactness of a number (is a property 
| that) should not be lost silently.

As Chris question/example illustrates this may be sufficiently messed up by
floats that the distinction may not be worth making. Dunno... Ive no definite 
opinion/data on that.  To put it simply float is such a grotesquely 
unmathematical type that it is unlikely to cooperate with clean orthogonal
distinctions such as
- Exact/inexact types are orthogonal to the rest of the number hierarchy
- Modelling converts a ‘real-world’ measurement/observation into a mathematical entity
- etc